Quantitative magnetic resonance angiography for flow quantification of carotid and intracranial stenosis

Abstract

Carotid and intracranial stenosis are responsible for stroke, which is the third leading cause of death globally. Carotid and intracranial stenting are used in management of stenosis. In-stent stenosis occurs in 25-35% of patients. Stent related artifacts and artificial lumen narrowing are problems during MRI scanning. A potential solution is estimate the flow profile across stenosis. The goal of this project is to optimize and implement quantitative magnetic resonance angiography (QMRA) for flow encoding and flow velocity estimation for better characterizing stenosis and assessing its degrees. We conducted multiple phantom measurements (mimicking normal carotid and middle cerebral anatomy) using phase contrast sequence with implementing different degrees of stenosis. Subsequent volunteer and patients measurements were conducted. In 8 mm tubes, flow was stable till 75 % stenosis while in 4 mm tubes, decline starts at 65% stenosis. In subject measurements, there is flow asymmetry between paired ICAs and MCAs that is not pathologic but within certain range. Patients had reduced flow in stenotic vessels compared to the other side and compared to mean flow in our volunteer subjects. QMRA results demonstrated reduced flow on the exact side detected with conventional MRA, with a strong correlation between QMRA and conventional MRA (R2 =0.7942). The percentage of flow difference between sides varied with the degree of stenosis. QMRA can be used for non-invasive diagnosis of suspected stenosis even if the stenosis itself cannot be visualized.